In the past two years, we have been increasingly exposed to the “cool” side of math: cryptography and encryption. Algorithms were not something you likely learned in school but most of us now understand, from Edward Snowden or The Imitation Game, that there are backdoors to computer codes.

Surprisingly, there is a Cold War era method of encoded communication, called a “numbers station,” which is unbreakable. It is cheap, largely untraceable, and has been used in South Florida for decades. However, it is a tool of the intelligence community which the United States has never admitted using — despite the fact that a numbers station appears to have been located in Palm Beach County.

A numbers station is a small shortwave radio transmitter which broadcasts bits of numbers on errant radio frequency which can be heard and decoded by agents in the field who know the frequency and the time to tune in. Many times, the voices are children or women, which add to the haunting, bizarre ritual. Some broadcasts, which went on for years, were given names such as “Atencion!” “Swedish Rhapsody,” and the (particularly spooky) “Lincolnshire Poacher.” You can hear samples of these broadcasts at http://bit.ly/numberwpb.

So how does a numbers station work? The broadcaster selects a frequency and specific times to broadcast. The recipient, or agent, tunes in using a commercial radio and decodes the message using a paper tablet called a “one time pad.” The broadcast begins with an “interval signal,” which is clip of music or other beacon sound that identifies that the code is about to begin. The (spanish) “Atencion!” numbers station is so named because of the female broadcaster’s insistent repetition of the word at the top of the broadcast. The Lincolnshire Poacher, on the other hand, begins with a few bars of an English folk song.

The code itself is typically a string of 150 numbers recited in groups of five at a time. The recipient uses the “one time pad,” which looks like a bingo card, and writes down the incoming numbers in a checkerboard fashion. By following the numbers on the top and side, the agent can decypher letters which spell words (the message). The page from the one time pad is then destroyed (burned), leaving no evidence. Since shortwave travels long distances (say, from Havana to South Florida) and radios are common, it is nearly impossible to locate the agents who tune in. Likewise, if the one time pad is properly destroyed, there is no evidence of transmission. If performed correctly, a numbers station transmission is simple and unbreakable.

The Cuban Intelligence Service (CuIS) has predominantly directed its agents to spy on the United States and has resorted to the use of numbers stations. Unfortunately for the CuIS, there have been a number of well-publicized spy blunders which led to convictions in the Southern District of Florida. Ten days after the September 11 attacks, Anna Montes was arrested for spying. The FBI affidavit stated that “CuIS often communicates with CuIS agents… by broadcasting encrypted messages at certain high frequencies” and noted that the FBI had been monitoring the Atencion! broadcast for years and found those codes on Ms. Montes’ computer. In 2006, an FIU professor and his wife, Carlos and Elsa Alvarez, were likewise caught spying via shortwave radio, water-soluable paper, and computer. Finally, in 2009, a State Department official, Kendall Myers, admitted to spying for 30 years via numbers station broadcasts. While, in each case, the spies were caught, it was due to human error (they used a computer to decode versus by hand) which leads to their capture.

Here in Palm Beach County, there is any number of intelligence-related operations, including the U.S. Navy AUTEC, which operates the “wargames” machine, the Electronic Warfare Threat Simulator. AUTEC is not much of a secret since it is the white building with satellite arrays at 801 Clematis Street.

More interesting is the Jonathan Dickinson Missile Tracking Annex which is an array of five massive satellites shrouded by the western edge of the Jonathan Dickinson State Park. Drive to Tequesta via U.S. One and then take a left on County Line Road. Pursuant to 50 USC 797 (the Subversive Activities Control Act), you cannot enter the Annex. And for good reason — according to GlobalSecurity.org, the Annex is equipped with a “command destruct system” which can be remotely activated by Cape Canaveral to shoot down a “launch vehicle” if it poses a danger.

Finally, there is the question of whether a numbers station existed in Palm Beach County. A notorious numbers station researcher, who used the moniker “Havana Moon,” claims that, in the late 1980s, he discovered a numbers station in Tequesta. Comparing those 30 year old directions to modern Google Maps, it appears that he was referring to the northern section of the Jupiter Inlet Lighthouse Natural Area. Heading north on US One, turn east on Beach Road and there is a small parking lot less than a half mile on the left side. Park there and head north for about 100 yards where you will discover a triangular shaped fenced area of U.S. Government property. On Google Maps, you can clearly see that this land was previously developed, including a square clearing in the northwest corner which appears to be the footprint of a former building. It is unclear why this abandoned-yet-protected federal land still exists in the middle of a secluded preserve. Sitting on a hill by the intracoastal, however, this would be a decent site to broadcast encrypted numbers.

Christopher B. Hopkins is a partner at Akerman LLP. Visit http://bit.ly/numberwpb for audio as well as photos of the (possible) former numbers station in Tequesta, Florida.